In wireless metropolitan area networks (WMANs) such as WiMAX, traffics in the uplink are usually short messages. For example, the short message may be an acknowledgement of a received packet, or a mouse click on a website, or a bandwidth request to send an email, or a beamforming matrix feedback due to a sudden channel variation, etc. These short messages are generated in a non-periodic or unpredictable fashion and thus it is hard for the base station to allocate resources (i.e. subchannels) for their transmission. In the current WiMAX systems, for example, either base station periodically polls the subscribers or the subscribers have to contend for the uplink resources to send the messages.
Both the polling and contention are inefficient and consume a significant system overhead. From channel coding perspective, the protection of short message is less efficient than that of the long message because the powerful channel codes require large block sizes. It is better to aggregate short messages and to encode them together.
Besides the increased overhead, the latency of the contention is unbounded, which is undesirable for delay sensitive applications. Although increasing the polling rate reduces the latency, the efficiency is also reduced because most of the polled subscribers do not have messages to send.
Thus, a strong need exists for improvements in existing schemes for short messages used in WMANS.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.